A metal material provided with an electric insulating film on a metal base material (also referred to simply as an insulating film in the present invention) is utilized in, for example, a circuit board as a shielding material (see, for example, Patent Literature 1). The metal material is suitable for a container, a case, a cover, a cap and the like, especially for a low height device container case (a height of an internal space is lowered).
In order to improve an adhesion between the metal base material and the insulating film of the metal material with the insulating film, there have been methods, in which a coupling agent is applied on a surface of a metal base material (see, for example, Patent Literature 2), or a plating layer having a dendrite crystal is formed on a surface of a metal base material (see, for example, Patent Literature 3).    Patent Literature 1: JP-A-2004-197224 (“JP-A” means unexamined published Japanese patent application)    Patent Literature 2: Japanese Patent No. 2802402    Patent Literature 3: JP-A-5-245432